sg_reset(8) - phpMan

SG_RESET(8) SG3_UTILS SG_RESET(8)

NAME
sg_reset - sends SCSI device, target, bus or host reset; or checks reset state

SYNOPSIS
sg_reset [--bus] [--device] [--help] [--host] [--no-esc] [--target] [--verbose] [--ver-
sion] DEVICE

DESCRIPTION
The sg_reset utility with no options (just a DEVICE) reports on the reset state (e.g. if a
reset is underway) of the DEVICE. When given a --device, --target, --bus or --host option
it requests a device, target, bus or host reset respectively.

A device reset is applied to the Logical Unit (LU) corresponding to DEVICE. It is most
likely implemented by a Low level Driver (LLD) in Linux as a LOGICAL UNIT RESET task man-
agement function.

The ability to reset a SCSI target was added in Linux kernel 2.6.27 . A LLD may send Low
level Drivers (LLDs) the I_T NEXUS RESET task management function. Alternatively it may
use a transport mechanism to do the same thing (e.g. a hard reset on the link containing a
SAS target).

In the Linux kernel 2.6 and 3 series this utility can be called on sd, sr (cd/dvd), st or
sg device nodes; if the user has appropriate permissions.

Users of this utility can check whether a reset recovery is already underway before trying
to send a new reset with this utility. Calling this utility with no options, just the DE-
VICE, will do such a check.

OPTIONS
-b, --bus
attempt a SCSI bus reset. A bus reset is a SCSI Parallel Interface (SPI) concept
not found in modern transports. A recent LLD may implement it as a series of resets
on targets that might be considered as siblings to the target on the DEVICE path.

-d, --device
attempt a SCSI device reset. This would typically involve sending a LOGICAL UNIT
RESET task management function to DEVICE.

-z, --help
print the usage message then exit.

-H, --host
attempt a host reset. The "host" in this context is often called a Host Bus Adapter
(HBA) and contains one or more SCSI initiators.

-N, --no-esc
without this option, if a device reset (--device) fails then it will escalate to a
target reset. And if a target reset (--target) fails then it will escalate to a bus
reset. And if a bus reset (--bus) fails then it will escalate to a host reset. With
this option only the requested reset is attempted. An alternate option name of
--no-escalate is also accepted.

--no-escalate
The same as -N, --no-esc.

-t, --target
attempt a SCSI target reset. A SCSI target contains one or more LUs. This would
typically involve sending a I_T NEXUS RESET task management function to DEVICE
There may be a transport action that is equivalent (e.g. in SAS a hard reset on
the link that contains the target).

-v, --verbose
increase the degree of verbosity (debug messages).

-V, --version
prints the version string then exits.

NOTES
The error recovery code within the Linux kernel (SCSI mid-level) when faced with a SCSI
command timing out and no response from the device (LU) does the following. First it tries
a device reset and if that is not successful tries a target reset. If that is not success-
ful it tries a bus reset. If that is not successful it tries a host reset. The "de-
vice,target,bus,host" order is the reset escalation that the --no-esc option attempts to
stop. In large storage configurations the escalation may be (very) undesirable.

This utility calls the SG_SCSI_RESET ioctl and as of lk 3.10.7 the --no-esc option is not
supported. Patches to implement this functionality may be accepted in lk 3.18 or 3.19 .

SAM-4 and 5 define a hard reset, a LOGICAL UNIT RESET and a I_T NEXUS RESET. A hard reset
is defined to be a power on condition, a microcode change or a transport reset event. LOG-
ICAL UNIT RESET and I_T NEXUS RESET can be requested via task management functions (and
support for LOGICAL UNIT RESET is mandatory). In Linux the SCSI subsystem leaves it up to
the LLDs as to exactly what type (if any) of reset is performed. The "bus reset" is SCSI
Parallel Interface (SPI) concept that may not map well to recent SCSI transports so it may
be a dummy operation. A "host reset" attempts to re-initialize the HBA that the request
passes through en route to the DEVICE. Note that a "host reset" and a "bus reset" may
cause collateral damage.

This utility does not allow individual SCSI commands to be aborted. SAM-4 defines ABORT
TASK and ABORT TASK SET task management functions for that.

Prior to SAM-3 there was a TARGET RESET task management function. And in SAM-4 I_T NEXUS
RESET appeared which seems closely related: the "I_T" stands for Initiator-Target.

Transports may have their own types of resets not supported by this utility. For example
SAS has a link reset in which both ends of a physical link (e.g. between a SAS expander
and a SAS tape drive) renegotiate their connection.

Prior to version 0.57 of this utility the command line had short options only (e.g. -d but
not --device). Also -h invoked a host reset while in the current version -h is equivalent
to --help and both -H and --host invoke a host reset. For backward compatibility define
the environment variable SG3_UTILS_OLD_OPTS or SG_RESET_OLD_OPTS . In this case -h will
invoke a host reset and the output will be verbose as it was previously (equivalent to us-
ing the --verbose option now). For example:

SG_RESET_OLD_OPTS=1 sg_reset -h /dev/sg1
sg_reset: starting host reset
sg_reset: completed host reset

ENVIRONMENT VARIABLES
Since sg3_utils version 1.23 the environment variables SG3_UTILS_OLD_OPTS or SG_RE-
SET_OLD_OPTS can be given. When either is present this utility will expect the older com-
mand line options as outlined in the NOTES section.

AUTHORS
Written by Douglas Gilbert.

COPYRIGHT
Copyright (C) 1999-2017 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

sg3_utils-1.43 October 2017 SG_RESET(8)

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